Zoom link : https://cnrs.zoom.us/j/95003883304?pwd=MI0B5WLYiGZlzo3oAZUl5TAu4fta6q.1
Context.
The solar corona exhibits a strong temperature inversion, with temperatures rising from the chromosphere to several million kelvin in the corona. Understanding how this inversion forms, known as the coronal heating problem, remains one of the central open issues in solar physics. Recent observations reveal that the upper chromosphere and the base of the transition region are highly dynamic, showing numerous short-lived and small-scale brightenings whose spatial distribution and temporal intermittency may play a key role in heating the overlying plasma.
Aims.
We investigate how spatially sparse and temporally intermittent heating events occurring at the base of the transition region contribute to generating the observed temperature inversion. This work extends a recently developed kinetic model by incorporating both spatial and temporal intermittency within a unified analytical description.
Methods.
The chromosphere–corona interface is modeled as a coarse-grained surface hosting stochastic heating events of characteristic size sH much smaller than s, which is itself much smaller than the solar surface area. By averaging the collisionless Vlasov equations for electrons and protons over this surface, we derive coarse-grained distribution functions fα that include the random spatial and temporal activation of heating. Heating events alternate between active and waiting phases of duration τ and tw, respectively, characterized by the parameters AS (spatial filling factor) and At (temporal duty cycle).
Results.
The stationary coarse-grained distribution remains leptokurtic and can be expressed through a single control parameter A = AS × At. The resulting temperature and density profiles reproduce the observed inversion, yielding chromospheric temperatures at the base and coronal values near 106 K for heating events of intensity ΔT much larger than the chromospheric temperature and A much smaller than 1. When microscopic dynamics is accessible, column-averaged temperatures depend separately on AS and At, while the transition region thickness depends only on their product.
Conclusions.
Spatially sparse and temporally intermittent brightenings at the base of the transition region can self-consistently produce the observed coronal temperature inversion. Both spatial and temporal intermittency act as complementary mechanisms for coronal heating within a unified kinetic framework.
